Basically, I'm looking for some do's and don'ts. Is it bad to keep my laptop plugged in when I'm not using it (majority of the time)? Is it bad to plug it in once I've finished using it (with it having something like 30% or 70% life left)?

This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.

However, it is important to note that Apple and Dell charging circuits may be different. Although, given that Dell does this, I assume Apple does as well. On this assumption, unless someone can provide sources to claim otherwise, I will assume that the Apple charging circuitry is smart enough to know this.

I encourage anyone to continue exploring this question and challenge my assumptions. Please see the sources below if you're curious for a more detailed explanation.

Laptop batteries' ideal life (from my experience) is around 2 to 2 1/2 years...I have a modern laptop around 2.5 years old, and the battery is already in questionable condition, even though it has been plugged in 90% of the time...Yes, it is true not to drain the battery completely, because it takes a charge cycle out of the life of the battery...

Honestly, if you are at your desk, and the battery is charged, I would recommend taking out the battery entirely. This way, you do not need to worry as much about it's life, at least in the long run.

Modern lithium-ion batteries nearly don't suffer the memory effect. But you should not drain it completely till your laptop powers of because there is no energy any more. Hard to happen under Windows, but perhaps if your computer is stuck booting, or your OS is crashed.
The main problem is heat. High temperatures increase the aging of batteries significantly.

It depends on the battery chemistry. That's true for NiCad, but bad for LiIon.
–
JRobertOct 10 '10 at 22:17

1

It should be noted that modern laptops practically always use LiIon batteries (or variants like Lithium-ion polmyer). I have never seen or heard of a laptop (less than 10 years old) that used anything else.
–
sleskeMay 12 '11 at 10:26